What will be the standard size for floor cushion?

Question:I want to get some floor cushion. But I'm confuse about size. I don't want it to be verry large. And I also worried about the material of cushion. Can anyone help me?

Answers:
3 feet by 3 feet. bean bags are great too! consider a material that is on the thick side so they dont wear off to quick. denim would be good or a thick canvas.